Symptoms

After a mailbox is moved to Microsoft Office 365 dedicated/ITAR (vNext), you can't connect to the mailbox by using an ActiveSync device.

Note If you use mobile device management software, some additional configuration may be required for migration. Please contact your vendor for guidance. If you don't use mobile device management software, the expectation is that a user will be prompted for credentials after the migration. They should specify their user principal name (UPN) to authenticate to Exchange vNext.

Cause

This issue can occur if there's a problem with an ActiveSync device.

Resolution

ActiveSync logging can be enabled by an end-user through Outlook Web App (OWA) or by an administrator through PowerShell. Please enable logging and then reproduce the connection behavior. Send the log to Microsoft for analysis.

Method 1: Users by using OWA

Ask the user to sign in to OWA, and then continue with to follow these steps.

In the upper-right part of the page, click Settings (), and then click Options.

In the navigation pane on the left side, expand General, and then click Mobile Devices.

From the list of devices, select the device that you want to track, and then click Start Logging.

In the Information dialog box, click Yes.

Reproduce the behavior that you want to capture, and then click Retrieve Log.

Note An email message that contains the log file (EASMailboxLog.txt) as an attachment is sent to your mailbox.

Method 2: Administrators by using PowerShell

Connect to vNext by using remote PowerShell.

Run the following command to enable ActiveSync logging for a specific user:

Note This command retrieves the statistics for the mobile device that's set up to synchronize with the mailbox of the user that you specified. In this example, the command also sends the log file to admin@contoso.com.